泡沫金属J积分试验的评价
An assessment of the J-integral test for a metallic foam
摘要：
通过有限元模拟与实验相结合，对开孔泡沫铝合金初始裂纹扩展的J积分测试程序进行了评估。实验发现，一个区域的随机失败的支柱发展领先的主裂纹尖端，是可比的塑性区的大小。因此，裂纹尖端J场是不存在的裂纹扩展的初始从主裂纹尖端。这意味着，尽管试样尺寸满足J有效性的通常标准，但测得的J_IC值和J与裂纹扩展Da曲线不能被视为材料特性。在单边缺口弯曲试样上进行了韧性试验，并通过直流电位降法、数字图像相关法和X射线计算机断层成像法测量了裂纹扩展。泡沫的裂纹扩展阻力与两个不同的塑性耗散区相关：（i）从裂纹尖端发出的体塑性区（包含一组随机失效的支柱），以及（ii）前进裂纹尖端后面的裂纹桥接区。的适用性的凝聚力区域模型预测断裂响应进行了探讨所观察到的情况下，大规模的桥接。要做到这一点，FE模拟是通过用可压缩的、弹塑性硬化的固体代替开孔金属泡沫的离散晶格来进行的，而泡沫中的断裂过程区由内聚区表示，其特征在于拉伸牵引与分离定律。的内聚区模型与实验观察的详细比较表明，它是可能的捕获的负载与位移响应，但不使用一组过程区参数的断裂过程区的细节。
英文摘要：
An assessment is made of the J-integral test procedure for initial crack growth in an open-cell aluminium alloy foam by combining finite element (FE) simulations with experiment. It is found experimentally that a zone of randomly failed struts develops ahead of the primary crack tip, and is comparable in size to that of the plastic zone. Hence, a crack tip J-field is absent at the initiation of crack growth from the primary crack tip. This implies that the measured J_IC value and the J versus crack extension Da curve cannot be treated as material properties despite the fact that the specimen size meets the usual criteria for J validity. The toughness tests were performed on a single-edge notched bend specimen, and crack extension was measured by the direct current potential drop method, by digital image correlation and by X-ray computed tomography. The crack growth resistance of the foam is associated with two distinct zones of plastic dissipation: (i) a bulk plastic zone emanating from the crack tip (containing a cluster of randomly failed struts), and (ii) a crack bridging zone behind the advancing crack tip. The applicability of a cohesive zone model to predict the fracture response is explored for the observed case of large scale bridging. To do so, FE simulations are performed by replacing the discrete lattice of the open-cell metallic foam by a compressible, elastic-plastic hardening solid while the fracture process zone in the foam is represented by a cohesive zone, as characterised by a tensile traction versus separation law. A detailed comparison of the cohesive zone model with experimental observations reveals that it is possible to capture the load versus displacement response but not the details of the fracture process zone using a single set of process zone parameters.
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